1. Field of the Invention
This invention relates to a plastic medical article and more particularly relates to a catheter of improved mechanical properties.
2. Background of the Invention
Substances which exhibit physical properties characteristic of a transition state between conventional liquids and solid are generally termed liquid crystals. The transition state is believed to be a result of an ordering of the molecules in melts and solutions of various organic compounds that occurs within certain ranges of temperature. The ordering is sufficient to impart some solid-like properties to the substances, but the forces of attraction usually are not strong enough to prevent flow. On the other hand, in those cases where a liquid crystalline substance is substantially solid in terms of flow, there are other fluid aspects of its physical state. This duality of physical properties is expressed in the term liquid crystallinity, or the synonymous term mesomorphism.
Some polymers are also known to exhibit liquid crystalline properties. These products have been disclosed for various applications, most particularly for molded parts which require high impact strength and for temperature sensing, recording and display devices. Representative of such disclosures are U.S. Pat. No. 4,814,211 to Buckley et al. and U.S. Pat. No. 4,841,014 to Brodowski.
Catheterization procedures conventionally include puncture of a patient's skin and insertion of a catheter into a body cavity, such as the blood stream, using some type of catheter insertion device. For maximum patient comfort, it is essential that the puncturing tip be as sharp as possible. It is also highly desirable that the catheter, and perforce any insertion equipment, be of the smallest possible cross-sectional area during insertion and use. It is nevertheless evident that the catheter lumen must be large enough to achieve the required rate of administration of a medicament solution through the catheter. Furthermore, for many applications, catheters are of great length and are extended along rather tortuous and extended paths within the body to reach desired locations. Accordingly, the ideal catheter would be stiff enough for insertion and manipulation inside a vein or artery without kinking, but at the same time be sufficiently soft and nonbrittle to avoid breaking off.
Catheters of the prior art have generally been made of polymeric materials such as polystyrene, polycarbonate, polyurethane and polyacrylate. These materials, while providing advantages for certain catheter applications, nevertheless have mechanical properties which limit their use for other applications. Accordingly, there is a need for a catheter having a balance of strength, stiffness and nonbrittleness suitable for insertion into a patient and maneuverability after insertion. The present invention addresses this need.